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1. ATC
2. TCAS
3. ATCRBS
4. PSR
5. SSR
6. db
LESSON 24
RADIO ALTIMETER
VOCABULARY
1. radio altimeter [ 'reidiou ][ æl 'timit ] 無線電高度表
2. vertical [ 'v:tikl ] a. 垂直的; 縱向的
3. absolute [ 'æbslu:t ][ 'æbslju:t ] a. 絕對的
4. terrain [ 'terein ] n. 地形;地面
5. frequency-modulated carrier 調頻載波
6. depth [ dep ] n. 深度
7. vary [ 'vri ] v. 變化;改變
8. dedicated [ 'dedikeitid ] a. 專用的
9. route [ ru:t ] n. 送往;送至
10. low range [ reind ] 低空
11. intend [ in' tend ] vt. 打算;企圖
12. principal [ ' prinspl ] a. 主要的
13. usage [ 'ju:zid ] n. 應用;使用;用途(法)
14. final approach [ 'fainl ][  'prout ] 最后進行
15. abbreviation [ bri:vi 'ein ] n. 縮略語;縮寫詞
16. LRRA = Low Range Radio Altimeter 低空無線電高度表
17. generation [ d en 'rein ] n. 產(發)生;形(生)成
18. reception [ ri 'sepn ] n. 接收(受)
19. is proportional to [ pr 'p :nl ] 與…成正比
20. interface [ 'intfeis ] n. ; v. 連接;接口
21. digital flight data recorder 數字飛行數據記錄器(黑匣子)
22. coax = coaxial [ kou 'æksil ] a. 同(共)軸的;共心的
23. keying pin [ 'ki:i ] [ pin ] 定位銷釘
24. insure [ in 'u ] v. 保證
25. orientation [ :rien'tein ] n. 取向; 定向(位)
26. identical [ ai' dentikl ] a. 相同的;相等的
27. interchangeable [ int 'teind bl ] a. 可互換的
28. approach [  'prout ] v. ; n. 進近; 接近
29. update [ p 'deit ] v. 更新
30. blank [ blæk ] a. ; n. 空白
31. standard readout [ 'stændd ]['ri:daut ] 標準讀數
32. dial [ 'dail ] n. 刻度盤
33. invalid [ in 'vælid ] a. 無效的
34. until [ n'til ] prep. ; conj. 直到…為止
35. release [ ri 'li:s ] vt. ; n. 釋放; 松開
36. delay [ di 'lei ] v. ; n. 延遲; 滯后; 延時
37. remain [ ri 'mein ] vi. 保持(…狀態); 保留
TEXT
[1] The radio altimeter system measures the vertical distance (absolute altitude)
from the airplane to the terrain. A radio altimeter is called "radio" because its
transmission is a continuous wave with constant amplitude and a
frequency-modulated carrier of 4300 MHz (c-band). The depth of frequency
modulation is 50MHz , so the transmission varies constantly between 4250MHz
and 4350MHz. Each R/T unit transmits radio signal to the ground through a
dedicated transmit antenna. The reflected radio signals are received by a
dedicated receive antenna and routed to the R/T unit for altitude computation.
The radio altimeter is called "low range" because it is not intended to operate at
airplane altitude above the ground greater than 2500 feet. Its principal usage is
during the final approach and take off. By the abbreviation LRRA, we mean
"Low range radio altimeter".
Fig. 24-1 LRRA system
[2] The low range radio
altimeter (LRRA) system
component locations are
as follow.
 The circuit breakers for
LRRA No.1 and No.2 are
located on the P18-1 and
P6-1 panels, respectively.
 Two receiver/transmitters
are located on the E2-4
shelf of the electrical/
electronic compartment.
 Two transmit and two
receive antennas are
located on the bottom
centerline of the airplane.
 The captain's EADI is
located on the P1 panel.
The first officer's EADI is
located on the P3 panel.
Fig. 24-2 LRRA component locations
[3]The LRRA R/T unit provides the required signal generation ,reception, and
processing necessary to measure the absolute height of the airplane above the
ground. The transmitted frequency range is 430050MHz. At some point in time
(t1), the transmitted frequency (f1) is transmitted to the ground and the reflected
signal received at the LRRA's mixer at time (t2). During the time interval (t),
the transmitted frequency has increased to a new frequency (f2). When the
frequencies f1 and f2 are mixed at time (t2), the output of the mixer is the
difference frequency (f) which is proportional to t and therefore to the
airplane altitude. This difference in frequency is converted to a dc voltage and
send to interfacing systems, these interfacing systems are EFIS symbol
generator, flight control computer, ground proximity computer, autothrottle
computer, and the yaw damper computer. The digital flight data recorder
receives the altitude data through the symbol generator.
　
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